Benzene ring, oxidation potential

With respect to the ring size, it has been stated that neither the redox potentials nor the half-lives of the Ni species are directly correlated to the cavity of the macrocyclic ligand, but the redox potentials are dependent on solvation effects.139 The effect of fused benzene rings and ring conformation has been monitored.140 In Ni complexes of fluorine-containing cyclams (25) the higher oxidation state becomes successively destabilized with respect to Ni, while the lower oxidation state (i.e., Ni1) becomes successively stabilized.141... 

Phenoxanthin, 68 X = S Y = O, is prepared by the electrochemical oxidation of diphenyl ether in dichloromethane and trichloroacetic acid containing tetraethyl-ammonium perchlorate at a composite anode of carbon and sulphur. The anode generates sulphur cations, which carry out electrophilic substitution on the benzene ring [237], Phenoxathiin radical-cation, formed at the potential of the fust oxidation wave, has been characertised by esr spectroscopy [238],... 

Annealing two benzene rings to the bpy framework leads either to biquinoline or isomeric Ao-biquinoline. Their respective complexes differ significantly in their redox behavior [74, 153, 227, 228] The first reduction of [Ru(biq)3] + is by 0.77 V more positive than that of [Ru(i-biq)3] +, in accordance with the trend in the reduction potentials of the free ligands. The difference between the oxidation and reduction potential for [Ru(biq)3] + is unusually small, 2.20 V, relative to [Ru(i-biq)3] +, 2.63 V, and most other Ru-polypyridines. 

In compound XXI, whose first irreversible oxidation peak potential is 0.47 V versus Ag/Ag, an S-S transannular interaction is likely to operate when compared with the oxidation potential, 0.7 V versus Ag/Ag" ", of l,8-bis(methylthio)naphthalene (XXIII). It is noteworthy to mention that 1,5-dithiocane (DTC), as in Eq. (40), the analogous saturated eight-membered ring compound of XXI, is oxidized reversibly, and it is suggested that the anchimeric assistance in oxidation of XXI and DTC is more effective in the latter [100]. When electrolyzed under controlled-potential conditions, XXI produces the corresponding monosulfoxide (80% yield). Cyclic voltammetric first peak potential of XXII was shown to be 400 and 670 mV, respectively, less positive than those of diphenyl sulfide and 1,3-bis[(methylthio)methyl]benzene [101]. 

There is a relationship between the structure and the ease of oxidation. Thus, the oxidation potentials become higher when the double bonds become part of benzene rings, as in LVI and LVII [188], Substitution by electron-donating groups lowers these potentials, as expected. 

---